1. Field of the Invention
The present invention relates to an image-holding member, more particularly to an image-holding member having an improved interlayer.
The present invention also relates to an electrophotographic apparatus, an apparatus unit, and a facsimile machine employing the above image-holding member.
2. Related Background Art
An image-holding member such as an electrophotographic photosensitive member which is repeatedly used for image formation is required to be capable of stably producing superior images with steady image density without fogging. The stabilities of the dark-area potential and the light area . potential as well as the stability of the sensitivity are highly important therefor.
In the modern electrophotographic photosensitive members which are constituted of an electroconductive support, a charge-generating layer formed thereon, and a charge-transporting layer formed further thereon, the charge-generating layer is usually extremely thin, having a thickness of 0.5 .mu.m or thereabout. Accordingly, the photosensitive member is liable to cause irregularity in sensitivity and potentials owing to defects such as stains, adhering matters, and scratches on the electroconductive support.
For the purpose of avoiding such disadvantages, it was proposed to provide an interlayer between a supporting member and a photosensitive layer, the interlayer having the functions of improving carrier injection from the supporting layer to the photosensitive layer, improving adhesion of the photosensitive layer to the supporting member, improving coating properties of the photosensitive layer, and covering defective spots on the supporting member.
Heretofore, known materials for the interlayer include polyamides (Japanese Laid-Open Patent Application Nos. 46-47344, 52-25638, and 58-95351), polyesters (Japanese Laid-Open Patent Application Nos. 52-20836, and 54-26738), polyurethane (Japanese Laid-Open Patent Application Nos. 49-10044, and 53-89435), casein (Japanese Laid-Open Patent Application No. 55-103556), polypeptides (Japanese Laid-Open Patent Application No. 53-48523), polyvinyl alcohols (Japanese Laid-open Patent Application No. 52-100240), polyvinylpyrrolidone (Japanese Laid-Open Patent Application No. 48-30936), vinyl acetate-ethylene copolymers (Japanese Laid-Open Patent Application No. 48-26141), maleic anhydride ester polymer (Japanese Laid-Open Patent Application No. 52-10138), polyvinylbutyrals (Japanese Laid-Open Patent Application Nos. 57-90639, and 58-106549), and quaternary ammonium salt-containing polymers (Japanese Laid-Open Patent Application Nos. 51-126149, and 56-60448), ethylcelluloses (Japanese Laid-Open Patent Application No. 55-143564), and so forth.
However, the electrophotographic photosensitive member having such an interlayer may vary in its electrophotographic properties depending on the environmental conditions such as temperature and humidity.
For example, the electric resistance of the interlayer tends to rise at a low temperature and a low humidity. Accordingly, electric charge is liable to remain in the interlayer to cause a rise in the residual potential and the light area potential, which tends to caused fogging of the formed images (in positive development) or to lower the image density (in reversal development). On the contrary, the electric resistance of the interlayer tends to fall at a high temperature and a high humidity. Accordingly, carrier injection from the supporting material to the photosensitive member is facilitated which results in decrease of the dark portion potential. Such a decrease which will lower the image density (in positive development). or will lead to formation of black-dot type defects (black spots) or fogging (in reversal development).
Furthermore, if the interlayer does not have sufficient solvent-resistance, the interlayer may dissolve or swell when a photosensitive layer is laminated causing deterioration of the electrophotographic properties.
With the demand for higher image quality in recent years, electrophotographic photosensitive members are being investigated which have stabler electrophotographic properties under a variety of environmental conditions from low-temperature and low-humidity to high-temperature and high-humidity.
The situation is the same for the other image-holding members used for display apparatuses, recording apparatuses, and light printing and plate-making.